title: Assessing the utility of infrared spectroscopy as a structural diagnostic tool for β-sheets in self-assembling aromatic peptide amphiphiles.
abstract: β-Sheets are a commonly found structural motif in self-assembling aromatic peptide amphiphiles, and their characteristic "amide I" infrared (IR) absorption bands are routinely used to support the formation of supramolecular structure. In this paper, we assess the utility of IR spectroscopy as a structural diagnostic tool for this class of self-assembling systems. Using 9-fluorene-methyloxycarbonyl dialanine (Fmoc-AA) and the analogous 9-fluorene-methylcarbonyl dialanine (Fmc-AA) as examples, we show that the origin of the band around 1680-1695 cm(-1) in Fourier transform infrared (FTIR) spectra, which was previously assigned to an antiparallel β-sheet conformation, is in fact absorption of the stacked carbamate group in Fmoc-peptides. IR spectra from (13)C-labeled samples support our conclusions. In addition, DFT frequency calculations on small stacks of aromatic peptides help to rationalize these results in terms of the individual vibrational modes.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow G1 1XL, UK.
authors.forename: Scott
authors.initials: S
authors.lastname: Fleming
authors.forename: Pim W J M
authors.initials: PW
authors.lastname: Frederix
authors.forename: Iván
authors.initials: I
authors.lastname: Ramos Sasselli
authors.forename: Neil T
authors.initials: NT
authors.lastname: Hunt
authors.forename: Rein V
authors.initials: RV
authors.lastname: Ulijn
authors.forename: Tell
authors.initials: T
authors.lastname: Tuttle
mesh_terms: D000409:Alanine / Q000737:chemistry; D005449:Fluorenes / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D011789:Quantum Theory; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: C496789:9-fluorenylmethoxycarbonyl; D005449:Fluorenes; D010455:Peptides; D000409:Alanine